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    <title>Document</title>
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<script>
    let arr=[1,2,3,4,5,4,3,2,1]
    //数组去重
    // let result =[...new Set(arr)]
    // console.log(result)

    //交集
    let arr2=[4,5,6,5,6];
    // let result=[...new Set(arr)].filter(item=>{
    //    let s2=new Set(arr2);
    //    if (s2.has(item)) {
    //        return true
    //    }else{
    //        return false
    //    }
    // })
 

    //交集简易版本
    //let result=[...new Set(arr)].filter(item=>new Set(arr2).has(item))

    //并集
    // let union=[...new Set([...arr,...arr2])]
    // console.log(union)

    //差集
    let diff=[...new Set(arr)].filter(item=>!(new Set(arr2).has(item)))
    console.log(diff)
</script>
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